Oerbier started it all for “The Mad Brewers” in 1980, when Herteleer and his brother took their homebrew to market as a riposte to the era’s watery beers and abbey knockoffs.

Still, the chestnut-tinged ale that is the brewery’s flagship combines the malt and power of a Trappist with tart notes evoking the region’s old red-browns. Yet this “original beer,” as its name implies, mimics neither.

The rest of the lineup is identifiably Belgian but remains unbound by the archetypes. There’s Arabier, no mere blond sibling, but strikingly bitter alongside the brewery’s trademark fruity malts; Stille Nacht, the Christmas bombshell with an acidity that can withstand long cellaring; Boskeun, a devilishly sweet Easter special; Dulle Teve, similar to a triple but assertively hopped; and the Stout, a massive example distinguished by the house’s signature tart note.

The wellspring of this creativity lies in Esen, West Flanders.

An 1835 brew house, rebuilt in 1921 after war damage, has gained a contemporary warehouse annex, both clad in the yellow brick from the clay of the polders, as locals call their lands reclaimed from the sea.

“The mad brewers”

Ancient art

Inside, there’s little of modernity. Mashing carries on in an open tun, and wort cools in the flat pan of a koelschip, its copper patinated green in places.Primary fermentation takes place in another open vessel, off-limits to visitors. Those who’ve seen it describe a cauldron of violent foaming and hissing, like a brew boiling itself.

Besides the conditioning tanks, a cellar tour arrives at the barrel room. This musty basement, with its own war history as a holding pen for prisoners, paradoxically represents a new element in the works.

In 2000, the brewery faced a crisis while transitioning between yeast supplies. With a batch of Stille Nacht exploding its bottles, Herteleer improvised a salvage operation by decanting into Bordeaux barrels, cadged from Cantillon. Two years later, the nearly forgotten brew was disinterred to the delight of a visiting group of brewers.

We don’t need to make new things all the time.

“Most inventions are discovered through unexpected circumstances,” he shrugs.

Barrel aging has given Herteleer room to play with Special Reserva versions of Stille Nacht and Oerbier. They pick up wine characteristics as well as oak tannins, developing flavours like a Vin Santo within distinct vintages. Other mistakes along the way have opened the door to wild fermentation, such as the Evil Arabier, a cult hit in America borne from a batch soured by bacteria.

These variants remain rare, alongside other experimentations that never leave the brew house. The product line-up remains fairly narrow for such an inventive, and now venerable, maker. “We don’t need to make new things every [time],” Herteleer explains, scoffing at breweries churning out new brands, different glassware, cheese accompaniments and other novelties.

“That’s boring. More than boring, it’s not critical at all. I will get a bottle of 2008,” he concludes — cutting off a discussion evidently so vapid, it must be washed away with a vintage Arabier. With its bitterness faded, aged to a refreshing tartness, it does the trick.